Cover for microtome and ultramicrotome freezing chamber

ABSTRACT

A transparent cover having a conical depression with an elliptical opening to control the passage of coolant gas from the freezing chamber of a microtome or ultramicrotome provides improved cooling with increased versatility and permits microtome techniques to be practiced heretofore not considered practical.

United States Patent mi Lechner [4 Aug. 13, 1974 COVER FOR MICROTOME AND3,495,490 2/1970 Dollhopf 83/9155 x ULTRAMICROTOME FREEZING CHAMBER IPrimary Examiner-William E. Wayner [75] Inventor: Gunther Lechner,Vienna, Austria Attorney, Agent, or Firm-Alan H. Spencer; William [73]Assignee: C. Reichert Optische Werke, AG, Nealon; Howard BerkenstockVienna, Austria [22] Filed: Sept. 5, 1973 [57] ABSTRACT [21] Appl. No.:394,593

[30] Foreign Application Priority Dat'a A transparent cover having aconical depression with 7 an elliptical opening to control the passageof coolant Sept. 6, 1972 Austria 7638/7 gas from the freezing chamber ofa micromme or tramicrotome provides improved cooling with in- 1.8. C-creased versatility and permits microtome techniques [5 Int. to bepracticed heretofore not considered practical [58] Field 0fSearch. 6 2/320; 83/9l5.5, 170, 171

I I I F. [56] References Cited 9 Chums 3 Drawmg gums UNITED STATESPATENTS 3,462,969 8/1969 Grasenick et al 83/9l5.5 X

COVER FORMICROTOME AND I ULTRAMICROTOME FREEZING CHAMBER BACKGROUND OFTHE INVENTION Freezing chambers for microtomes and ultrami'crotomesgenerally comprise a rectangular box shaped. chamber with an externalcontrol and coolant supply. The chamber may be cooled to a pre-selectedtemperature, which may be as low as about -l60C, by the controlledevaporation of a liquid coolant such as nitrogen. One, and usually twoor three, evaporation units are lo cated in the chamber. Preferably, oneunit is so located as to cool the knife and one unit is so located as tocool the specimen arm with an optional unit toassist the first two inrapidly cooling the chamber- Two basic techniques have been heretofore.used. A

closed freezing chamber is conventionally used when it' is possible tosupport, by a float liquid, specimens as they are cut. Such floatliquids must be selected from materials which remainliquid at theselected temperature and dimethyl sulfoxide mixed with water is anexample of such a float liquid. It is apparent that the liquid, ormixture of liquids, selected must not only remain liquid at the selectedtemperature, but should not react with or otherwise adversely affect thespecimens cut. The closedchamber is the most efficient and effectivedevice since the escape of the coolant is restricted and effects ofvariations inthe medium surroundingthe chamber are notsignificant.However, severe limitations caused by interaction betweenthe float liquid and specimen as well as providing float liquids whichdo not freeze at extremely low temperatures significantly restrict theusefulness of closed chamber devices. British patent No. 1,170,796'isone example of such a device and discloses someof the problems inherenttherein.

The open chamber is used for thedry knife technique which requiresremoval of specimen sections as they are cut. This technique is usedwhen sections may react with or be otherwise affected by liquids used tofloat sections as described above. The open chamber is substantially thesame as the closed chamber with the top removed to permit access toremove the sections as they are cut. Such chambers are extremelyinefficient since the unrestricted flow of gas escaping from the opentopped chamber requires large quantities of coolant to maintain evennominally reduced temperatures in the area of the specimen and knife.Such open chambers are also highly susceptible to fluctuations intemperature caused by air currents in the room, opening of doors and thelike. The aforementioned'British patent further discloses disadvantagesof an open type chamber including the formation of ice crystals causedby condensation from the surrounding medium.

BRIEF DESCRIPTION OF THE PRESENT INVENTION AND DRAWINGS It is one objectof the present invention to provide a freezing chamber overcoming thedisadvantages of the prior art chambers.

It is a further object of the present invention to provide a freezingchamber having the advantages of the closed chamber as well as theadvantages of the open chamber, while substantially eliminating orminimizing the disadvantages of each.

It is still a further object of the present invention to provide anefficient freezing chamber substantially unaffected by variations in thesurrounding medium and using substantially less coolant than prior artopen chambers. I

The freezing chamber of the present invention is distinguished by itscover having an elliptical opening in a conical depression in the cover.The elliptical opening is defined by a plane bisecting the conicaldepression at an anglewith respect to the cover and positioned toprovide working access to'remove sections as they are cut whilesumultaneously minimizing the escape of coolant by having the area withthe greatest depression near the rapid cooling unitof the freezingchamber to deflect the evaporating liquid away from theopening.

FIG. 1 is atop view of a freezing chamber in perspective;

FIG. 2 is a top view of the cover for such a chamber; and

FIG. 3 is a side view in cross-section of the cover.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a chamberbody 1 of a conventional insulating material has a knife holder 2mounted therein. Knife 3 is held in the holder by clamp 4 which may bemanually tightened by locking screw 5. Knife adjustments are made byconventional micrometer means 6. Specimen arm 7 has a specimen clamp 8mounted thereon to carry a specimen 9 to be sectioned. The specimen armextends through an opening 10 in the side of body 1 and the opening isclosed by flexible seal '11: which permits movement of the arm 7 duringthe cutting operation. Coolant for the knife is introduced through inlet12 and conducted to knife cooling unit 13 by tubing 14. Specimen arm 7is cooled by unit 15 which is connected by passage 16 with coolant inlet17. Rapid cooling unit 18 is connected to the coolant supply via tubing19*and inlet 20 primarily to assist units 13 and 15 during the initialcooling cycle.

The selected reduced temperature for the sample is obtained byintroducing coolant such as liquid nitrogen through inlets 12, 17 and 20to cooling units 13, 15 and 18- where heat is absorbed by evaporation.The cooling units and controls therefor may be of a conventional typeincluding those taught in the aforementioned British patent and arewell-known to those skilled in the art.

Cover 21, in FIG. 2, has an ellipsoidal opening 22 located therein atthe base of a conical depressed area 23-.-.The' edge 24 of depressedarea 23 which defines opening 22 is asymmetrically located and in aplane which bisects cover 21 at an angle of about 5 to 15. Referring toFIG. 3, the location of opening 22 and the angle a of plane 25 provide amajor lip area 26 and a minor lip area 27. The larger depression in area26 deflects the gas evaporating from rapid cooling unit 18 away fromopening 22 without significant restriction of operator manipulatingspace within the area of the cutting knife. Similarly, gas evaporatingfrom the specimen cooling unit 15 is deflected away from the opening.Deflection of gas evaporating from cooling unit 18 and opening.Deflection of gas evaporating from cooling units 18 and 15 increases theefficiency of the cooling chambers by causing the cool gas to force warmgas from the chamber in the minor lip area 27 without significant directloss of gas from these cooling units. Gas evaporating in knife coolingunit 13, which is closed, is vented through tubing 28. In a chamberhaving approx imate dimensions of I50 millimeters X millimeters pressionhaving a major base axis of approximately l2 l millimeters and a minorbase axis of 82 millimeters is formed with the-major and. minor axesbisecting sub stantially in the centerof the cover are satisfactory.

The edge of the depression lies in a plane which bisects the cover at anangle of approximately 95 to produce a major-lip having a maximum depthof about 20 millimeters from the cover surface and a minor lip having amaximum depth of about millimeters from the cover surface. Thesedimensions provide desirable flow paths and restriction of gas escape ina chamber of theselected chamber temperature, the flow is generallybetween 0.07 grams per second to 3.5 grams per second for thetemperatures from about 0C to l60C from each of cooling units 13 and 15.Since cold nitrogen is heavier than room temperature air, the air israpidly displaced through the window as the chamber fills with cold gasand the formation of condensation ice is prevented by the displacementof moisture containing air.

, The window opening, being of a proportional size to the chamber volumeand gas flow substantially elimi the knife and specimen theimprovementcomprising I acover for said chamber, said cover having anupper surface, a conical depression in said upper surface, saiddepression having a continuous depending sidewall and a lowermost edgedefining a passage through said cover, said edge being spaced from saidupper surface and being in a plane bisecting the plane of said uppersurface at an angle less thanabout l5 whereby the flow .of evaporatinggas within said chamber displaces the atmosphere through said passagefrom the chamber without significant mixing.'

,2. The improvement of claim 1 wherein said cover has a rectangularperipheral border, said conical depression said passage have major andminor axes.

3. The improvement of claim 2 wherein said major axes are coincident.

4. The improvement of claim 3 wherein said passage is egocentricallydisplaced within said depression.

5. The improvement of claim 4 wherein the ratio of the planar area ofthe chamber closed by said cover to the planar area of said depressionto the planar area of said passage is about 120.5 0.2.

' 6. The improvement of claim 5 wherein said angleis about 10.

7. The improvement of claim 6 wherein the distance between saidlowermost edge and said upper surface nates mixing of air with thecoolant within the chamber during the cooling and/or cutting operations.

I claim:

1. in a freezing chamber for a microtome or ultramicrotome having acooling unit to absorb heat by the evaporation of a liquefied gas in anarea proximate to andsaid passage.

9. The improvement of claim 8 wherein said chamber has a plurality ofcooling units.

1. In a freezing chamber for a microtome or ultramicrotome having acooling unit to absorb heat by the evaporation of a liquefied gas in anarea proximate to the knife and specimen, the improvement comprising acover for said chamber, said cover having an upper surface, a conicaldepression in said upper surface, said depression having a continuousdepending sidewall and a lowermost edge defining a passage through saidcover, said edge being spaced from said upper surface and being in aplane bisecting the plane of said upper surface at an angle less thanabout 15* whereby the flow of evaporating gas within said chamberdisplaces the atmosphere through said passage from the chamber withoutsignificant mixing.
 2. The improvement of claim 1 wherein said cover hasa rectangular peripheral border, said conical depression said passagehave major and minor axes.
 3. The improvement of claim 2 wherein saidmajor axes are coincident.
 4. The improvement of claim 3 wherein saidpassage is egocentrically displaced within said depression.
 5. Theimprovement of claim 4 wherein the ratio of the planar area of thechamber closed by said cover to the planar area of said depression tothe planar area of said passage is about 1:0.5 : 0.2.
 6. The improvementof claim 5 wherein said angle is about 10*.
 7. The improvement of claim6 wherein the distance between said lowermost edge and said uppersurface varies continuously between a maximum and a minimum providinglarge and small portions of said sidewall.
 8. The improvement of claim 7wherein the large portion of said sidewall is intermediate said coolingunit and said passage.
 9. The improvement of claim 8 wherein saidchamber has a plurality of cooling units.